Incandescent lamp and its manufacture



Jan. 24, 1939. C B,RDSEYE ET AL I2,144,673v

INcANDEscENT LAMP AND 1Ts MANUFAGTURE Filed Ogl.. 5l, 1935 fig. SilverCov/fing A figg. 7.

Molded Base Maer/'a/ Panarea Jan. 24, 1939 UNITED sTliTlazsV anatraINCANDESCENT LAMP AND ITS MANUFACTURE Clarence Birdseye and PincusDeren, Gloucester, Mass., assignors to Birdseye Electric Company,Gloucester, Mass., a corporation of Delaware Application October 31,1935, Serial No. 47,581

11 Claims.

This invention relates to the manufacture of incandescent lamps and moreparticularly to such lamps in which the bulb is provided with areflecting ksurface for increasing the amount of light from such asource available for useful In the manufacture of incandescent lamps ofthe kind having a reflecting lamp bulb certain of the light rays fromthe bright filament of the l0 lamp are intensified by refiection from -arefiecting surface formed by-silvering a part of the wall of the bulb.For direct lighting the filament is hooded by the reflector, the lowerlimit of the silvered area being preferably-at such a distance from thefilament that all of the rays emanating from thefilament, both directand refiected,

eventually will `leave the lamp Within a predeabove, below or at oneside of the filament accord-x ing to the position of the lamp when inuse and the above described relation of the boundary of the reflector tothe filament may be varied considerably for indirect lighting, where thearea o'f the illuminated field may profitably be very greatly increased.It has been found that in by the use of a reecting bulb and in the caseof direct lighting there is the further advantage of having theintensely bright spot of -the filament effectively removed from thefield of vision.

In developing a commercially successful refleeting bulb for incandescentlamps several diiculties Were encountered and largely overcome but inthe solution other disadvantages developed which this inventionhaseliminated.

One part of the problem was tov eliminate from the useful eld of lightany projected image of the filament. Such a projection of a distortedimage of the filament, thereby making a very bright area in theilluminated zone is due to the l fact that the filament is preferablylocated at or near what may be described as the focus of the reflectingsurface of the bulb. Heretofore, the solution of this problem has beenattempted by frosting the lower or useful light emitting area of thebulb below the silvered or reiiecting area, or

above it, in the case of lamps having the lower portion of the bowlsilvered. This treatment will' diffuse the useful light to a certainextent and so 60 tend to eliminate the discordant bright area, but

either case the emciency of the lamp is increasedk with considerableincreased loss of light, as explained below.

Another part of the problem was to eliminate any tendency of the lamp tocast a shadow of the filament near the center of the brightlyilluminated field due to the reected light impinging in part on thefilament itself. This shadow tends to center with the reflected image ofthe bright filament, but because of the irregularity and non-symmetry ofthe parts of the filament and because they are not located at any truefocus of the reflecting area, the shadow and the bright image do notregister but `there is built up a zone that is of different brilliancythan the rest of the illuminated area, most of which is brighter butwith a mottling of shadow. A diffusion of the emitted light by frostingas above described has heretofore been resorted to in an attempt tosolve this problem, and with similar introduction of losses.

Frosting the area of the bulb through which light is emitted has aserious disadvantage in that the high concentration of the bright rayspassing through the frosted glass tends to unduly raise the temperatureof the glass due to the absorptive power ofthe frosting, and thisincreased loss as heat represents a substantial loss of useful light.

One object of the present invention is to in` crease the eiciency ofreiiecting lamps by eliminating high-lights and shadows within theuseful lighting zoneall without decrease in intensity of either thedirect or reflected light rays from the source of light.

In achieving this object a new method is employed of producing adiffused light from a highlamp, thus neutralizing any distinct focusingeffect and producingv a substantially uniform intensity of illuminationthroughout the lighted area without loss of efcicncy'. The employment ofthis new method permits the manufacture of reecting bulb incandescentlamps with clear glass below the reflecting area thus allowing all ofthe light rays, in undiminished brilliancy, to illuminate the usefulfield.v

This invention, in its broader aspects, embraces within its field thediffusion of light through the medium of a diffusing reflector incontradistinction to the diffusion of vlight by transmitting through adiffusing body. A particular application relates to diffusing the lightfrom reecting bulbs so as to eliminate from the illuminated field eitherthe partially focused image or the shadow of the filament or othersource of light.

In order that the later use of the term diffusing reflector may beunderstood the distinction between reflected light with and withoutdiffusion should be'borne in mind. In an ordinary or plane reflectorlhaving a smooth reflecting surface or mirror the angle of incidence isalways equal to the angle of reflection from the particular point underconsideration. When the reflecting surface is not a single plane, forexample a curved surface, these angles are measured with respect to aplanetangent to the surface at thepoint in question. Thus at any pointon such a curved reflecting surface the light rays are still directlyreflected and at all points the two angles are always equal. Such smoothreflectors provide specular reflection.

In a diffusing or non-specular reflector the angle of'reflection at anypoint on the surface may be any angle whatever with respect to thegeneral contour or surface plane of the reflector. 'I'hat is, althoughby chance certain rays and beams may be reflected at the angle ofincidence, practically all of the rays and beams falling on a diffusingreflector will be reflected at an angle different from the angle ofincidence with respect to the surface plane of the reflector. Adiffusing reflector will therefore have a very large number of minute ormicroscopic surface irregularities which individually may form almostany angle whatever with the plane of the reflector as a whole. Each ofthese microscopic surface irregularities acts as an individual mirrorand the angles of incidence with respect to the surface plane of thereflector and reflection from each individual mirror are, of course,equal. Reflected light from such a mirror is diffused, that is it leavesthe mirror in almost all possible directions.

A specific application of the invention in commerce is to incandescentlamp bulbs having a portion of the wall of the bulb prepared as a highlyefficient diffusing reflector. The lamp bulb may be of the conventionalshape or of almost any special shape and yet gain a pronouncedbeneilcial effect by having some part of its surface acting as adiflusing reflector. In any application of the invention to lamp bulbsthe surface of that part of the wall of the bulb acting as the reflectormay have been modified either at the time of making the bulb or by asubsequent treatment enabling diffusion of light, or modified by thekind of reflecting surface applied to create a diffusing reflector, itsroughened, irregular or uneven reflecting surface being formed eitherbefore or after or during the operation that produces the reflectoritself.

In the past, difficulties have been encountered in producing anefficient, durable and attractive reflecting silver film on the innersurface of an evacuated glass vessel or one to be evacuated. Thesediilliculties are no doubt responsible for the fact that prior to mywork no satisfactory insidesilvered lamp bulb was commerciallyavailable. One difficulty was that it was found impossible to make asilver fllm ladhere evenly and uniformly to the inside surface afterevacuation. The silver could be deposited by any well-known process, butwhen the bulb was thereafter evacuated, bubbles would make theirappearance in the silver fllm which, on bursting, would permit thesilverito peel off the glass wall.

It was subsequently discovered that the difficulty was due to a physicaland possibly chemical change of the surface layer of the glass, afterwhich change the layerreadily occluded gases because of its more spongynature. The usual cleaning processes employed in the art produced littleor no effect on this layer, so that upon evacuating the bulb, theoccluded gases would expand and give rise to the bubbles which destroyedthe continuity of the silver film.

In copending application, Serial No. 42,227, filed September 26, 1935,Pincus Deren describes the mentioned difllculties and discloses a methodof eliminating this injurious gassy layer without affecting thetransparency of the bulb, by a variation of the well-known etchingprocess. It is also a part of our invention to eliminate the gassy layerprior to silvering, but, since my primary interest is in a diffusingsurface and my'preferred means for obtaining it is to etch or frost theinner surface of the bulb prior to silvering, we may use any commonetching or frosting solution, preferably one giving a good even andunlform frost with no marked depressions.` When,

on the other hand, we desire to deposit silver on a smooth transparentsurface, we may utilize the etching solution disclosed by Deren for thispurpose. In either case, the etching process serves to remove theobjectionable gassy layer and prepare the inner surface of the bulb forreceiving the deposited silver in such a way that after sllvering andevacuation, a fine, attractivesilver fllm is obtained having no holes,bubbles or peeled spots. By depositing the silver upon a roughened orfrosted glass surface we have found that the film adheres very strongly.

A further problem arises in the case of inside frosted bulbs by reasonof the fact that the inside frosting process seriously weakens theglass, presumably by the formation of myriads of minute crevices at thebottom of which the thickness of the glass is below the safe limit. Inthe past it has been necessary to give to inside frosted bulbs a secondetching and strengthening treatment which necessarily adds to the costof production. Such a strengthening treatment, now widely employed inthe manufacture of insidefrosted non-reflecting bulbs, is disclosed inU. S. Letters Patent No. 1,687,510, to Pipkin.

We have found that such second strengthening treatment is. whollyunnecessary in the case of my inside frosted, silvered bulbs, becausethe silver film coats the sharp crevices and strengthens the surface.Our inside frosted silvered bulb, though given no other strengtheningtreatment, is adequately strongi for shipment and commercial use ingeneral.

The objects of the invention and the features and methods through whichthey are attained will best be understood and appreciated from thefollowing description of the best embodiments at present known asillustrated in the accompanying drawing.

The figures of the drawing are sectioned for glass as the base materialfor the reflector but this is for illustration in connection with a useof the invention in incandescent lamps and is not to be construed aslimiting. In the drawing;

Figures l and 2 show, respectively, a pre-treatment of the base materialby frosting and a reflecting medium is then applied to such frostedface, as by silvering;

Figs. 3 and 4 show, respectively, one face of the base material preparedfor retaining an irregular surfacing of the reflecting medium and suchsurfacing then applied;

Figs. 5 and 6 show, respectively, a modification of the treatment shownby Figs. 3 and 4 in that the prepared base material is given its unevenreflecting surface by a special treatment thereof;

Figs. 'I and 8 show, respectively, a modification of the treatment shownin Figs. 1 and 2 in that the base material is first molded to an Aunevenmatrix prior to applying a reflecting medium to a face thereof:

Fig. 9 is illustrative of an incandescent lamp provided with a diffusingreflector made in accordance-with the teaching of this specification;and

Fig. 101s a view of an incandescent lamp similar to Fig. 9 but showing amodified form of reflector for reflecting both diffused andynon-diffused light.

Referring to the drawing, l0 represents a 4section of' a suitable l basematerial for a reflector or for a mirror which may be a part of theglass bulb of an incandescent lamp. The four pairs of figures from 1 to8 illustrate fou'r methods of procedure to produce a diffusing reflectoron the base material. These will be described in their application tothe production of reflecting lamp bulbs as a specific example of usewithin the broader scope of the invention.

Method I (Figs; 1 and 2) The interior of the bulb may be frosted by apre-treatment with hydrofiuoric acid in the manner regularly employed inthe industry for ordinary non-reflecting bulbs except that a singleetching process is suillcient as above described.

The frosted area may be the entire inside surface of the bulb, or it maybe co-extensive with the reecting surface, or it may be of less extentthan the reflecting surfaceV which will be obtained by silvering at alater operation. It is preferable, from the standpoint of efficiency. toleave the light transmitting area of the bulb unfrosted but for certainpurposes it may be desirable to frost the light transmitting part of thebulb beyond the diffusing reflector, so that the bright filament willnot be directly visible from any'angle. A thin coating of metallicsilver deposited on the microscopically roughened surface forms arougher matte surface than when deposited on the smooth glass; in factit pax-takes almost exactly of the nature and contour of the minutecraters and pin holes which have been etched into the surface of theglass by the hydroluorlc acid. While the surface appears to bemacroscopically smooth the rugosities thus formed are readily visibleunder the microscope.

This minutely lirregular surface of metallic silver is still silver andit still 'reflects with the high coefficient of reflection that anysilvered surface does, but it reflects a diffused light.

The coating resulting from this method of 'solving the problem gives awhite appearance to the outside of the bulb, even whiter than anunsilvered frosted bulb. For certain purposes this may well be anadvantage in that the bright diffusing reflector is not visible throughthe glass.

Under some conditions, as in the case of an asymmetric bulb designed fora special purpose, it may not be dsirable or necessary to form a lightdiffusing surface over the entire area of its reflector. In such a casethe reflector would consist of a combination of selected areas forrefiecty tages it is not the preferred method. There is always thedanger of the unprotected silver becoming defaced, as by scratching,during .the period of use, and it will tarnish and eventuallydeteriorate. A protector against these eventualities may be provided butthis is expensive and for many uses undesirable. Moreover the light,

in order to be reflected from the silvered outside surface of the bulb,must rst pass through the glass and in the case of inside frosting mustpass through the glass twice. 'Ihis causes a real loss of lightingemciency.

Method II (Fig. 3 and 4) disclosed in the mentioned Deren application,and l then at the end of the period when an adequate deposit of the finecrystals has taken place, the shaking motion imparted to the bulb andits contents is stopped. and the continued deposition of silver isallowed to proceed while the bulb is at rest. This builds up arelatively thick and irregular deposit upon the rst coating whichappears under the microscope to be composed of large crystals, andcrystal masses. vThese large relatively irregular crystals have the sameexcellent high coefficient of reflection as any other pure silvercoating, Abut are actually sufficiently large and irregular to reflect adiffused light. It has been found that this relatively coarse crystaldeposit adheres better to the glass if it is deposited upon a finercoating of silver, but this method is not limited to this combination oflayers since satisfactory diil'using reflectors may be made by a coatingof coarse silver crystals directly onto the base material.

Method III (Figs. 5 and 6) This method consists in depositing a regularfine coating of metallic silver, as described in said co-pendingapplication Serial No. 42,227 of Pincus Deren, and then making thisrelatively smooth surface somewhat coarser and rougher by attacking itwith a chemical substance that will change part of the silver to acompound of silver. Since the very fine crystals of which the metallicsilver layer is composed fit very closely together, and may even overlapin places, it is vapparent that by changing some of these crystalsand/or parts of some of these crystals to a compound containing agreater weight of matter and of lower specific gravity than the heavymetallic' silver, the volume of the silver coating will be considerablyincreased. This effect will be manifest by an irregular raising of partsof the surface of the deposit and the development oi' what appear to belarger crystals. 'Ihe color of the deposit may change somewhat,depending on what the treatment is. For example, if the freshly silveredbulb is filled with a solution of sodium chloride there will be agradual change of the surface layers of the silver coating from silverto silver chloride. Red phosphorous in water suspension introduced intothe bulb will gradually attack the surface oi the silver deposit,particularly if a trace of nonoxidizing mineral acid, for examplehydrochloric. is added to the water. Air containing a very lowconcentration of chlorine, or other halogen, may

be admitted. into the dry bulb and again part of the silver deposit ischanged to silver chloride.

Method 1v maar and s) This method of forming a highly efficient reectorproducing diffused light may be carried 'out 4 andere by using specialmolds or matrices in which the bulbs are blown. Any repeated pattern ora series ofageometric lines may be cut into or raised upon the bulbmold, such as a pattern made by forcing ties of frosting, can then havea thin smooth coat c' of metallic silver applied thereto and as thisprovidesy a roughened or uneven refiectingu'surface Y a diffusingreflector will result.

Adifi'using reflector made under any of these methods greatly increasesthe amount of diffused light emanating from such a reflecting surfaceoccupying a definite and predetermined part of the surface of the bulbof an incandescent lamp, and so avoids either the projection of apartially focused image of the filament ory its shadow, and

without necessarily causing the light to be transmitted through afrosted or otherwise diffusing surface with its consequent loss ofefficiency. y

This difference in'lighting efllciency is shown by the followinglaboratory data, typical of many such comparisons that have been made.The bulbs of the two lamps compared were as nearly alike as possible inall respects, except that the bulb of lamp B was frosted over thelight-transmitting, non-silvered area only, and the bulb of lamp A wasfronsted under the silvered area only. Both were 150 watt reflecting anddiffusing lamps, but lamp A obtained diffusion by reflecting from adiffusing inside reflector with a microscopically 40 roughened surfacethe light being transmitted through unfrosted glass, while lamp Breflected from a bright plain inside reflector and obtained diffusion bytransmitting the light through frosted glass. 'I'he light falling on thetest table was substantially equally diffused and both luminous fieldswere substantially uniform as to intensity of illumination. y l

The lamps were tested in the same socket, permanently fastened at aconstant distance above 5o the test table. The actual foot-candles rofil lumination falling on the table were measured directly under the lampand at one half foot distances measured in a straight line along thetable away from this point.

- Lamp A dlf- Dimnf "331 omt fusing-reflector Lamp ll frosted overtransi rfcty u er amp type, iootmittng area, foot-candles n candles 000.o- 4s. o 41.0 0. 50. 0 42. 0 i. 42.5 41.0 1.. 37. 5 37. 5 2. 33.0 31.5 2. 27. 5 26. 0 3. zi. 5 22. (l 20.0 18. 1S. 0 14. 0 14. 5 12. 0 11. 510. 0 9. 5 8. 0

120 120 Current require- 1.265 1.275 ments oi lamps 161.8 153.0 duringthe test.

Thus, in this comparison, despite the fact that the prior art lamp B,obtaining diffusion by trans- 75 mitting through a frosted area, was ofslightly higher wattage rating, it actually emitted less light. The sumof the foot-candles in each of the columns is a rough comparativemeasure of the total amount of light emitted. On cornpar-K ing thesesums it is apparent that the newdif-v v fusing-reflector lamp `A of thisinvention emits about 10% more light than the old reflecting anddiffusing lamp B.

While silver has been named as a metal suitable' for a reflectingcoating it isy contemplated y10 that other metals may beemployed withinthe scope of the invention. For example, nickelrnay be used, or chromiummay be deposited upon a thin priming coat of silver. f

Fig. 9 of the drawing shows an application of 15 the invention to anincandescent rlamp used yfor direct lighting. As illustratedthe-diffusing rey sector l2 is of sufficient depth no hood the mament i4the lower boundary of the reflector being so located relatively to thefilament that the 20 light rays may spread to an approximate 60 cone,indicated by dotted lines, hereinbefore described as having been foundto constitute an eflicient fleld of useful light. With the use, of adiffusing reflector the portioni ofthe bulb wall 25y through which thelight shines may be clear glass as shown. The figure shows a reflectingdisk il, preferably of metal, and located between the'flla-` f ment andseal of the lamp serving, among other functions, to reinforce the usefullight emitted 30 by deflecting the rays or beams heretofore lost in theneck of the lamp, as disclosed in the co l pending application ofClarence Birdseye Serial No. 33,694, flied July 29, 1935whlch is Patent2,142,104. This reflecting disk, when used with sa the diffusingreflector I2, would also preferably be convertedto a diffusing reflectorby one of the methods described herein or its equivalent.

Fig. 10 illustrates, byway of example, an incandescent lamp providedwith a reflector that 4o reflects a diffused light from one part and anondiffused light from another part. The bulb shown is provided with aninside diffusing reflector I2 like that shown in Fig. 9 and with anadded plain or specular reflector 20 in the form of an annulus 45 at thelower edge of the reflector I2. The position of the specularlyreflecting portion withrer y f lation to the diffusing portion may bevaried. It may be added to or it may partly impinge upon or be whollysurrounded by the diffusing reflector according to the conditions underwhich the lamp is to be used, for example, spot lighting a particularobject or increasing the illumination over a special area.

When the specularly reflecting portion is in the position shown in Fig.10, namely, an annulus at or about the region of greatest diameter ofthe bulb, it serves to increase the illumination over a ring at theperiphery of the illuminated field where it would otherwise be less thanat the a0 center. At the same time it also serves to narrow the fieldsomewhat. The net effect is to give a more uniform illumination over anarrower fleld instead of a less uniform illumination over a widerfield. When the specularly reflecting portion is 35 otherwise disposedit gives a different effect, predictable from its position relative tothe filament.

From the foregoing description and from the appended claims it will beunderstood that dif- 10 fusing reflectors to be manufactured from theteaching of this invention arenot limited as to size, shape or location-with respect to the source of light and may be employed with lampsvarying widely in type and power. In its application u or capable ofdiffusing light simultaneously with its reflection from a reectingsurface, particularly an internal reflector and light diffuser.

It is believed that a reflector of this type, having a surface. of highreflective index and with this surface minutely roughened in a mannerreadily discernible under a microscope, and for the purpose ofreflecting a diffused light from a high temperature concentrated source,and without transmitting thisl reflected light through a diffusingmedium which always incurs losses, has not been heretoforeavailable.

The nature and scope of the invention having been indicated andpreferred embodiments and methods of manufacture having beenspecifically described, what is claimed as new, is:-

1. The method of making light diffusing lamps having a high temperaturesource of light which comprises applying a substantially smooth coatingof silver to a. surface of the lamp and then treating the exposedsurface of said coating in a manner to create -surface rugosities.

2. The method of claim 1 in which the said treatment consists insuperimposing an irregular deposit of relatively large silver crystalsand silver crystal masses on said first coating of silver.

3. The method of claim 1 in which the said treatment consists inattacking the outer layers of said coating with a chemical capable ofconverting the treated parts to a compound of silver 3,-,` therebyobtaining an uneven development of larger` crystals throughoutthetreated parts and thus raising such parts irregularly above the surfaceof said coating.

4. The method of claim 1 in which the said treatment consists inincreasing the volume of the silver in said coating throughout parts ofits surface thereby raising said parts above the surface of saidcoating. n f

5. The method of making light diffusion lamps having a high temperaturesource of light which comprises coating a surface of the lamp with adeposit of silver crystals sufficiently large and irregular to produce asurface capable oi' reflecting a diffused light. 6. An incandescent lampincluding in its structure a'bulb and alight source and having ametallic reflecting medium applied to the inner surface of part of thevarea of the bulb, the reflecting medium having its exposed surfaceuneven so that light reflected thereby isl diffused, said n innersurface ofthe bulb to which the reflecting medium is applied beingsmooth and even and the exposed surface of the Vreflecting medium beingrough and uneven.

7. Anv incandescent lamp having a reflecting disc positioned between thesource of light and the seal of said lamp, said disc havingitsreflecting surface roughened by minute irregularities so that itreflects a diffused light.

8. An incandescent lamp having a reflecting disc positioned between thesource of light and the `seal of said lampand having a reflecting mediumapplied to a predetermined area of its bulb, the reflecting surfaces ofboth disc and bulb reflecting -a diffused light by virtue of minuteirregularities extending thereover.

9. An incandescent lamp comprising a bulb,

having a lament-of concentrated. spiral form therein, the inner surfaceof said bulb being provided with a. reflecting surface from a point onthe neck of said bulb to the region of greatest diameter of said bulb,an annular portion of said reflecting surface in the region ofgreatest'dlameter of said bulb being specularly reflecting in characterand the remainder of said reecting surface being diiusely reflecting incharacter, the lament being placed substantially at the Afocus of saiddiifusely reflecting portionlof said reflecting surface, and the planeangle subtended at the filament by that boundary of the specularly'reflecting surface which is furthest from the neck of said bulb beingsubstantially degrees.

10. An incandescent lamp as in claim 9 in which the'dlifusely reflectingsurface consists of a nlm of metal of substantially uniform thicknessadhering closely to the roughened inner wall of the bulb.

11. An incandescent lamp as in claim 9 in which the diifusely reflectingsurfaceI consists of a film of metall adhering to the smooth inner wallof the bulb, the exposed surface of said film being rough. I

CLARENCE BIRDSEYE. PINCUB DEBEN.

